The performance of color printers and color copying machines has progressed considerably in recent years. As a result, society began suffering from forgery of printed matter using such machines. For example, currency notes, paintings, tickets, and pre-paid cards are most likely to be targeted for forgery and illegal use. Because of this risk of forgery, there is now a demand for forgery resistant and illicit-use protected printed matter, as well as systems for creating such printed matter.
One art recognized means of prevent forgery or illicit use is to password protect documents using magnetic strips, bar codes or the like. However, as society gets more and more complex, individuals are required to memorize more and more confidential data, such as passwords, for daily activities. Accordingly, the realization of a handy system, which does not use any computer or electronic device yet readily protects such confidential information, has been long awaited.
One example of such system is found in the Applicants' International Publication No. WO 00/19365, which is incorporated herein by reference. This publication discloses a card system wherein each card has a legal cardholder's photo picture printed on the card surface in such a way that confidential information is hidden in the printed picture, and only the legal card holder can restore the confidential information out of the picture. However, as is the case with all traditional image-based steganographic and watermarking techniques, which are also known as image deep layer cryptography and electronic scorch-out techniques, this system requires the use of information hiding techniques on computer data. In this case the information-hidden image data is saved in computers as a file, or transmitted through computer-networks as a file.
The drawback of this type of system is that once a printing device prints out the information-hidden image data, the confidential information cannot be subsequently extracted, as the accuracy of the printed image by a printing device is insufficient, and as the image reading device (i.e., image scanner) cannot restore the image data exactly. For this reason, both traditional steganographic techniques and watermarking strategies do not satisfy the social demands as described above and, therefore, printed image based steganography or watermarking techniques have heretofore been avoided.
Accordingly, there is a need for printed matter that is self-authenticating and for information hiding system that will produce printed matter from standard printing devices in which embedded confidential information, such as authenticating information, may be extracted.